Coloring of textiles



United States Patent O COLORING OF TEXTILES Werner A. Schoeneberg, Murray Hill, and Paul A. Studer, Millburn, N.J., assignors to C'elanese Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 23, 1955, Ser. No. 548,766

6 Claims. (Cl. 8-24) This invention relates to the coloring of textile materials and relates more particularly to the coloring of textile materials containing fibers of cellulose esters of low hydr'oxyl content.

It is an object of this invention to provide a new and useful method for the coloring of textile materials composed of blends of cellulose fibers and fibers of cellulose esters of low hydroxyl content.

Another object of this invention is the provision of a novel method for the coloring of textile materials composed of the aforesaid blends, in which both the cellulose fibers and the fibers of cellulose esters of low hydroxyl content are colored in the same uniform, full shade and in which the colored textile material is highly resistant to crocking and to fading when washed or when exposed to sunlight.

Still another object of this invention is to provide an economical continuous process for the coloring of textile materials composed of the aforesaid blends.

Other objects of this invention will be apparent from the following detailed description and claims. In this de scription and claims all proportions are by weight unless otherwise indicated.

In accordance with one aspect of this invention a vat pigment is deposited on the surface of a textile material composed of a blend of a cellulose fiber, such as cotton, and a fiber of a cellulose ester of low hydroxyl content. Thereafter the textile material is given a heat treatment to cause the vat pigment to penetrate into the cellulose ester of low hydroxyl content. A reducing agent is then applied to the textile material to convert the vat pigment on the cellulose fiber to the leuco form which, in contrast to the oxidized or pigment form, has a substantive affinity for said cellulose fiber. The textile material may then be treated in well known manner to oxidize said leuco form in the cellulose fiber.

The cellulose esters of low hydroxyl content employed in the process of this invention contain not more than 0.29, preferably zero to 0.12, alcoholic hydroxyl groups per anhydroglucose unit in the cellulose molecules thereof. Best results are obtained by the use of cellulose acetate of very high acetyl value, e.g. an acetyl value of at least 59%, preferably 61 to 62.5%, calculated as combined acetic acid. However, other lower aliphatic acid esters of cellulose of low hydroxyl content may be employed. Examples of such esters are cellulose propionate, cellulose butyrate, cellulose acetate-propionate, cellulose acetate-butyrate and cellulose acetate-formate.

Any cellulose fiber may be employed in the blends which are treated in accordance with this invention. Examples of cellulose fibers are cotton, ramie, sisal, viscose rayon, cuprammonium rayon or the fibers produced by saponification of stretched cellulose acetate filaments. When cotton is employed it is preferably mercerized before the vat pigment is applied to increase its afiinity for the leuco vat. Such mercerizing treatment does not adversely affect the cellulose ester of low hydroxyl content in the blend being treated.

Amanthrene Vat Pink FFD (Pr. 109), Ponsol Blue Green Y.

Advantageously the vat pigment is deposited by applying to the textile material an aqueous dispersion of particles of said coloring material, as by a padding or printing operation. The aqueous dispersion may also contain a dispersing agent, such as one or more of the following substances: a soap, e.g. sodium oleate, a sulfonated alkyl benzene, e.g. sulfonated decyl benzene, a sulfated long chain fatty alcohol, e.g. sodium lauryl sulfate, a polyalkylene oxide derivative'of a long chain fatty material, e.g. a polyethylene glycol monoether of oleic acid, a lignosulfonate, or a sulfonated formaldehyde-naphthalene condensation product. The concentration of the coloring matter in the aqueous dispersion and the amount of the aqueous dispersion applied to the textile material may be varied, depending on the desired depth of shade. Mixtures of vatpigments may be employed to produce any desired mixed shades.

Where it is desired to apply the coloring material to selected areas only of the fabric in order to produce a pattern thereon, it is advantageous to employ the coloring material in the form of a relatively viscous printing paste, which may contain a thickener. Any of the usual types of thickeners are suitable. Thus, for aqueous printing pastes there may be used such water-soluble thickeners as glue, vegetable gums such as gum tragacanth or gum arabic, cellulose derivatives such as methyl or hydroxyethyl cellulose, polyvinyl alcohol and alginates such as sodium alginate. In the practice of this invention it is preferable to use those dispersing and thickening agents which do not discolor under the conditions of the subsequent heat treatment.

After the vat pigment has been deposited on the tex-' tile material the material is preferably dried and then subjected to the heat treatment, which, as stated, causes penetration of the pigment into the cellulose ester. Substantially none of the pigment becomes incorporated into the cellulose ester material prior to the heating step. That is, practically no actual coloring or dyeing of the cellulose ester material takes place during the step of depositing the coloring material thereon, the coloring r r1a terial being deposited in such a condition that it can be removed by simply scouring prior to the heat treatment.

The heat treatment of the textile material may be carrred out in air or in any other convenient gaseous or inert liquid atmosphere or even in vacuum or in a liquid which does not dissolve or remove the applied pigment. Thus, the textile material may be passed through a hot air oven or through a bath of a suitable liquid such as a molten metal of low melting point. Heat may also be applied by means of infra-red radiation or a high frequency electric field. For best results, during the heattreatment the textile material should, attain a surface temperature of about 400 to 450 F. and should be heated for a relatively short time, e.g. 5 to seconds. The exact temperatures and times of treatment will depend to a large extent on the heating medium and also on the weight and construction of the textile material. It will be understood of course that the heat treatment is preferably not continued for such a long period as to cause substantial degradation of the textile material. H

The heat treatment employed in the process of this invention has the further advantage of improving the physical properties of the textile material. Thus, it cf I fects an improvement in the safe ironing point, the resistance to glazing, the resistance to shrinkage on pressing with moist steam, the ability of the material to be pleated permanently, and the resistance of the material to mussing or wrinkling on laundering. For example, the heat treatment causes the safe ironing temperature of a fabric of a cellulose acetate of acetyl value 59% or above, calculated as combined acetic acid, to be raised at least C., and preferably at least about 40 C., e.g. from about 180 C. up to 220 C. or 240 C. or higher.

After the heat treatment the cellulose fibers of the blend still carry particles of the vat pigment, there being little if any migration of this pigment from said cellulose fibers to the cellulose ester fibers during the heat treatment. When the reducing agent, previously mentioned, is applied to the textile material these pigment particles are converted to their soluble leuco form.

The treatment with reducing agent and the subsequent oxidation of the leuco form of the vat dye may be carried out in accordance with any of the procedures commonly used for the vat dyeing or vat printing of cotton or rayon. Thus, any of the well known reducing agents for vat dyes may be used in the practice of this invention. An aqueous solution of sodium hydrosulfite has given excellent results. Other reducing agents which may be employed are sodium formaldehyde sulfoxylate, zinc formaldehyde sulfoxylate, and sodium bisulfite plus zinc dust. It is ad vantageous to use a markedly alkaline reducing medium (e.g. a solution containing 1 /2 ounces of NaOH per gallon) and, in certain cases, to incorporate a suitable dispersing agent such as Nekal NF, Ahcovat VL or Peregal ST with the reducing agent, as well as to add some glucose to prevent subsequent premature oxidation of the leuco form of the vat dye. Depending on the time of treatment, a suitable temperature for the reducing bath is about 120 to 200 F. The reducing agent may be applied in any desired manner, for example by passing the textile material through an aqueous bath containing the reducing agent dissolved therein, for example in a continuously operating Williams Unit reducing range or, particularly when printed fabrics are being treated, a pad steaming range.

The treatment with alkaline reducing agent tends to strip off any vat pigment remaining on the surfaces of the cellulose ester fibers, but it does not substantially affect either the physical characteristics or the color of said cellulose ester fibers. Excessively high concentrations of alkali in the reducing bath may, at times, cause surface saponification of the cellulose ester fibers.

The oxidation of the leuco form of the vat pigment may be effected by any of the procedures well known for this purpose in the dyeing industry. Thus there may be used any suitable oxidizing medium such as alkaline hydrogen peroxide, sodium perborate or sodium nitrite acidified with sulfuric acid and after oxidation the dyed textile material may be soaped hot to remove surface dye and to stabilize the shade of the dyeing.

The process of this invention lends itself readily to continuous operation. In one suitable procedure, a textile fabric is passed continuously and successively through a padder where the vat pigment is applied, then through a drier and a heat-treating unit such as a radiant heat oven, then through a bath of reducing agent and thereafter through a bath of the oxidizing agent.

The process of this invention may be applied to all sorts of textile materials such as yarns, circular-knitted or warp-knitted fabrics, woven fabrics and fabrics made up of randomly arranged fibers.

The following examples illustrate this invention further.

Example I A woven fabric composed of a blend of 70% of fibers of cellulose acetate of 61.5% acetyl value, calculated as combined acetic acid, and 30% of cotton fibers is mer- Pink FFD, the prototype of which is identified by formula at page 564 of The Chemistry of Synthetic Dyes and Pigments, by Lubs, published 1955 by Reinhold Publishing Company, 2.5 grams per liter of tetrasodium pyrophosphate, 1 gram per liter of the wetting agent Nekal NS and 2.5 grams per liter of the wetting agent Tamol N at a temperature of 120 F. The fabric, carrying about of its weight of this dispersion, is dried at a temperature of 200 F. and then passed through an infra-red radiant heater where it remains for seconds and where its surface temperature is raised to 450 F. Thereafter the fabric is passed through a Williams Unit reduction range where a heated aqueous reducing bath containing 16 grams per liter of caustic soda, 20 grams per liter of sodium hydrosulfite and 1 gram per liter of tetrasodium pyrophosphate at a temperature of 190 F. is applied thereto for 20 seconds. The fabric is then rinsed with water, oxidized with an aqueous solution containing 1 60. per liter of aqueous 30% hydrogen peroxide, 1 cc. per liter of aqueous 56% acetic acid for about 20 seconds at F., and thereafter soaped at the boil with an aqueous solution containing 1 gram per liter of soap and 1 gram per liter of Peregal ST (polyvinyl pyrollidone).

The resulting uniformly colored pink fabric is fast to washing, as shown by the fact that it passes the #3 A.A.T.C.C. wash-fastness test involving washing at F. It is free of crocking and it shows only a very slight change in shade after exposure to light in a fadeometer for 40 hours.

Example II Example I is repeated except that the dye used is Indanthrene Golden Yellow RKA which is identified by structure at pages 448 and 449 of The Chemistry of Synthetic Dyes and Pigments, by Lubs, published 1955 by Reinhold Publishing Company. The washfastness and lightfastness of the resulting yellow fabric is substan tially the same as that of Example I.

Example III Examples I and II are repeated except that the fabric is a blend of 50% of the cellulose acetate of high acetyl value and 50% of viscose rayon. The results are substantially the same as those described in Examples I and II.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the coloring of blends of cellulose ester fibers and cellulose fibers, comprising applying a vat pigment to a blend of cellulose fibers and cellulose ester fibers, the latter containing at most 0.29 hydroxyl group per anhydroglucose unit in the cellulose molecules thereof, then heat-treating, at a temperature of 400 to 450 F., the blend to cause said vat pigment to penetrate into said cellulose ester, thereafter subjecting said blend to a reducing agent to convert the remaining vat pigment on said cellulose fibers to its leuco form, and thereafter oxidizing the resulting leuco vat dye on said cellulose fibers.

2. Process as set forth in claim 1 in which said vat pigment is applied to said blend in the form of an aqueous dispersion thereof.

3. Process as set forth in claim 1 in which said reducing agent is applied to said blend in the form of an aqueous dispersion thereof.

4. Process as set forth in claim 1 in which the heat treatment is continued fora time sutficient to raise the safe ironing temperature of said cellulose acetate fibers by at least about 20 C. and to improve their resistance to glazing and to shrinkage on pressing with moist steam.

5. Process as set forth in claim 4 in which said cellulose acetate has an acetyl value of at least about 61%.

6. Process for the coloring of fabrics, comprising padding an aqueous dispersion of a vat pigment onto a fabric woven of a blend of fibers of cellulose acetate of at least about 61% acetyl value and fibers of cellulose, heat-treating said fabric at a fabric temperature of 400 to 450 F. to cause the vat pigment to penetrate into said cellulose acetate, then passing the fabric through an aqueous alkaline solution of sodium hydrosulfite containing a levelling agent for leuco vat dyes, and thereafter oxidizing the resulting leuco vat dye in said fabric.

References Cited in the file of this patent UNITED STATES PATENTS 893,384 Schlegel July 14, 1908 5 2,080,254 Dreyfus May 11, 1937 2,385,403 Conaway Sept. 25, 1945 2,663,612 Gibson Dec. 22, 1953 OTHER REFERENCES Man-Made Textiles, October 1957, vol. 34, No. 401,

pp. 67-68. 15 Du Pont Tech. Bulletin, September 1955, pp. 115-120. 

1. PROCESS FOR THE COLORING OF BLENDS OF CELLULOSE ESTER FIBERS AND CELLULOSE FIBERS, COMPRISING APPLYING A VAT PIGMENT TO A BLEND OF CULLULOSE FIBERS AND CELLULOSE ESTER FIBERS, THE LATTER CONTAINING AT MOST 0.29 HYDROXYL GROUP PER ANHYDROGLUCOSE UNIT IN THE CELLULOSE MOLECULES THEREOF, THEN HEAT-TREATING, AT A TEMPERATURE OF 400 TO 450*F., THE BLEND TO CAUSE SAID VAT PIGMENT TO PENETRATE INTO SAID CELLULOSE ESTER, THEREAFTER SUBJECTING SAID BLEND TO A REDUCING AGENT TO CONVERT THE REMAINING VAT PIGMENT ON SAID CELLULOSE FIBERS TO ITS LEUCO FORM, AND THEREAFTER OXIDIZING THE RESULTING LEUCO VAT DYE ON SAID CELLULOSE FIBERS. 